A mimicking network for a k-terminal network, N, is one whose realizable external flows are the same as those of N. Let S.k/ denote the minimum size of a mimicking network for a k-terminal network. In this paper we give new constructions of mimicking networks and prove the following results (the values in brackets are the previously best known results): S.4/ D 5 [216], S.5/ D 6 [232]. For bounded treewidth networks we show S.k/ D O.k/ [22k ], and for outerplanar networks we show S.k/ · 10k ¡ 6 [k22kC2].